[0001] This invention is concerned with a bearing assembly comprising a housing having a
bore, a bearing which is disposed in the bore and a shaft which is supported by the
bearing for rotation with respect to the housing.
[0002] The bearing may be a rolling element bearing, such as a spherical roller bearing,
with an inner ring, an outer ring and a plurality of elements arranged to roll on
the raceways of the two rings.
[0003] Conventional housings for use with rolling element bearings have, up until now, broadly
uniform radial stiffness. Hence the resultant load path, that is the portion of the
outer or inner bearing ring raceway onto which the rolling elements contact and transmit
the load to or from the inner ring raceway, is positioned over one part of the periphery
of the outer ring or inner ring raceway when the bearing is subjected to a radial
load.
[0004] The use of a single load path is the hitherto commonly accepted load pattern and
all the current bearing performance predictions are based on this assumption. However,
disadvantages arise with a single load path arrangement particularly in situations
which require the bearing to provide lateral stiffness (that is stiffness across the
axis of the bearing) and where vibration free operation is required.
[0005] The current practice is to attempt to achieve these requirements by introducing a
degree of pre-load into the bearing, that is, to at least remove all clearance between
the rolling elements and the respective inner and outer ring raceways.
[0006] To obtain an optimum degree of pre-load within a bearing can be difficult, time consuming
and costly with the desired result not being fully achieved as basically a single
active load zone still exists for carrying the radial load. This method is in the
main a compromise condition and the degree of pre-load is uncertain and difficult
to maintain.
[0007] Patent Specification GB-A-2008451 (Georg Fischer) discloses a bearing assembly which
utilises a dry running bearing having pads which are continuously adjustable by means
of an hydraulic flow and control circuit to vary the pre-load. This manner of pre-loading
to achieve stability of the shaft is used where the subsequent movements are small
in magnitude and/or slow in speed.
[0008] In other more dynamically demanding applications, clearance with the bearing surfaces
are necessary to accommodate expansion of the components resulting from the heat generated
within the bearing from the loads carried and the speed of operation. GB-A-2008451
cannot provide the requirements of lateral stiffness and vibration free operation
in these dynamically demanding applications, besides being a complicated and expensive
system.
[0009] Patent Specification JP-A-62-124317 (Application No. 60-262531) (Shinano) uses a
ring between an outer ring of a ball bearing and the bore of a housing, which ring
has two radially inner projections. However, this ring is made of an elastomer such
as rubber and in the dynamically demanding applications envisaged would not provide
the requirements of lateral stiffness and vibration free operation.
[0010] The invention provides a bearing assembly comprising a housing which has a bore,
a bearing which is disposed in the bore and a shaft which is supported by the bearing
for rotation with respect to the housing, characterised in that the bearing is supported
by at least two portions of differing stiffness, the or each less stiff portion being
arcuate and centred on the bearing axis, such that the reaction to a load acting along
a radius of.the bearing includes substantial components to each side of that radius
which are opposed to each other.
[0011] With such an arrangement, the reaction components give greater and predictable lateral
control than an arrangement in which the reaction to the load is aligned with the
radius.
[0012] By supporting the bearing itself, rather than having the support as being part of
the bearing the required type of bearing with the desired pre-load can be chosen for
the particular application. The designed internal clearance (or pre-load) within the
bearing is not disturbed.
[0013] Preferably, the housing includes a portion which is radially less stiff or more resilient
than adjacent portions and is in line with that radius. The less stiff or more resilient
portion cannot provide the complete or full reaction to the radial load so in effect
splitting the reaction into more or less discrete parts.
[0014] The stiffness of this portion should be in the order of two or three times less than
that of adjacent portions.
[0015] Preferably, the housing includes a sleeve, the less stiff portion being an integral
part of a sleeve. This construction allows simple and economical production in which
a sleeve or bush is machined to provide a recess such as a longitudinally extending
groove so forming a less stiff portion.
[0016] Preferably the less stiff portion is provided by a recess which is radially spaced
from the bearing. This feature allows a simple and economical realisation of the less
stiff portion.
[0017] The recess may be positioned radially outside of the bearing for the case in which
the load is transmitted from the shaft to the housing by way of the bearing, and may
be positioned radially inside of the bearing for the case in which the load is transmitted
from the housing to the shaft by way of the bearing.
[0018] Preferably, the less stiff portion extends longitudinally of the bearing and is unsupported
at its ends. This construction ensures that the load acts along the complete length
so eliminating any bowing effect along the length of the less stiff portion.
[0019] Preferably, the radial thickness of the less stiff portion is 0.15 × the sectional
height of the bearing. The sectional height of a bearing is the radial distance from
the bore to the outer surface. Also, the less stiff portion preferably subtends laterally
an angle of 50° from the longitudinal axis of the bearing.
[0020] In the accompanying drawings:
Figure 1 is part of a longitudinal section of a bearing assembly;
Figure 2 is part of a section on II-II of the assembly shown in Figure 1;
Figure 3 is a cross-section of another bearing assembly; and
Figure 4 is a cross-section of a further bearing assembly.
[0021] Figures 1 and 2 show a bearing assembly comprising a housing 10 having a bore, a
bearing 11 which is disposed in the bore and a shaft 12 which is supported by the
bearing for rotation about its longitudinal axis with respect to the housing. The
bearing 11 has an outer race ring 13, an inner race ring 14 and a series of rolling
elements 15 arranged between the race rings to roll on their raceways. The bearing
11 has a sectional height 16 which is the radial distance between the inner surface
of the inner ring 14 and the outer surface of the outer ring 13.
[0022] The bearing 11 is mounted directly on the shaft 12 and is seated in the bore of a
cylindrical sleeve 17 secured as a tight/accurate fit in the housing 10. In use of
the assembly, a load P is transmitted from the rotating shaft 12 to the housing 10
by way of the bearing 11 and the sleeve 17. For the purposes of illustration, the
load P is considered to act along a radius of the bearing 11 and to be constant in
magnitude and direction. The sleeve 17 is provided with an arcuate recess 18 which
is in its outer surface and so radially spaced from the bearing 11 and is in line
with the radius along which the load P acts. The recess extends longitudinally of
the sleeve 17 and forms an arcuate portion or strap 19, which is unsupported at its
ends and centred on the axis of the bearing. The strap 19 is less stiff or more resilient
than the rest of the sleeve - of the order of two to three times less radially stiff;
and subtends an angle A of 50° at the longitudinal axis of the bearing. With the cross-sectional
thickness of the housing wall supporting the bearing outer ring 13 being of the same
order as the sectional height 16 of the bearing 11, the strap 19 has a radial thickness
20 in the order of 0.15 × the sectional height 16.
[0023] Because of the strap 19, the load zone has two lobes with centres lying approximately
35° on each side of the radius along which the load P acts. The forces in these lobes
of the load zone have maximum peak reactions R₁ and R₂ acting radially of the bearing
11, where

[0024] These two reactions R₁ and R₂ can be resolved into components C₁₁, C₁₂ and C₂₁, C₂₂
respectively, with C₁₂ and C₂₂ being opposed and directed towards each other.
[0025] Thus, compared with a uniform load zone in a conventional bearing assembly, the resulting
load is reduced by 39% so leading to an increased load bearing capacity.
[0026] The dimensions of the bearing 11, in particularly, the number of rolling elements
15, and the size of the angle A are chosen so that there are a sufficient number of
the elements for transmitting load all the time in use of the assembly along the radial
lines of action of the reactions R₁ and R₂.
[0027] To ensure that the sleeve 17 is fitted in its correct position, the housing 10 and
the sleeve 17 are provided with bores. When the bores are aligned, the sleeve 17 is
in the correct position and a pin 21 is then inserted to maintain the sleeve in position.
[0028] The bore of the sleeve 17 is finish machined, either before or after being fitted
to the housing 10, to a diameter suitable to accommodate the bearing 11.
[0029] Figure 3 shows basically a similar construction as that shown in Figures 1 and 2,
with a housing 30, a bearing 31 and a shaft 32. The bearing 31 has a sectional height
33.
[0030] In use, a load P is transmitted radially from the shaft 32 to the housing 30 by way
of the bearing 31. In this construction, there is no sleeve and the cross-section
of the housing is significantly larger than the sectional height 33 of the bearing
31. The housing 30 has an arcuate recess 34 which is radially spaced from and on the
outside of the bearing 31 and is in line with the radius along which the load P acts.
The recess 34 extends longitudinally of the bearing 31 and forms an arcuate portion
or strap 35 centred on the bearing axis. The strap 35 has a radial thickness 36 in
the order of 0.15 × the sectional height 33 and subtends an angle A of 50° at the
axis of the bearing 31. There are reactions R₁ and R₂ to the load P.
[0031] The construction shown in Figure 4 comprises a housing 40 having a bore, a bearing
41 which is disposed in the bore and a shaft 42 which is supported by the bearing
for rotation about its longitudinal axis with respect to the housing. The bearing
41 is a rolling bearing with a sectional height 43. The bearing 41 is seated directly
in the bore of the housing and mounted on a cylindrical sleeve 44 which is mounted
as a tight/accurate fit on the shaft 42.
[0032] In use of the assembly, a load P is transmitted from the rotating housing 40 to the
shaft 32 by way of the bearing 41 and the sleeve 44. The sleeve 44 is provided with
an arcuate recess 45 which is in its bore or inner surface and so radially spaced
from the bearing 41 and is in line with the radius along which the load P acts. The
recess 45 extends longitudinally of the sleeve 44 and forms an arcuate portion or
strap 46 which is un-supported at its ends and centred on the bearing axis. The strap
46 subtends an angle A of 50° and has a radial thickness 47 in the order of 0.15 ×
the sectional height 43 of the bearing 41. The strap 46 is less stiff or more resilient
than the rest of the sleeve 44 - of the order of two to three times less radially
stiff.
[0033] Because of the strap 46, the load P has two radially acting reactions R₁ and R₂,
of which the maximum peak is 0.61P. When these reactions R₁ and R₂ are resolved into
right angled components, two of the components are opposed to each other and act in
opposite directions so laterally supporting the bearing 41.
[0034] To ensure that the sleeve 44 is fitted and maintained in its correct position on
the shaft 42, the sleeve and shaft have radial bores. The sleeve 44 is in its correct
position when the bores are aligned, whereupon a pin 48 is inserted and secured.
[0035] In summary, the constructions described and illustrated reduce the effective contact
load on the raceway and roller elements; reduce the vibration within the bearing by
spreading the load over a greater number of roller elements; and increase lateral
stability by the reaction forces from the generated load zones.
[0036] In another aspect, each bearing is in effect supported at the corners of the recess,
so causing the spread in the load.
1. A bearing assembly comprising a housing (10;30;40) which has a bore, a bearing
(11;31;41) which is disposed in the bore and a shaft (12;32;42) which is supported
by the bearing (11;31;41) for rotation with respect to the housing (10;30;40), characterised
in that the bearing (11;31;41) is supported by at least two portions (19;35;46) of
differing stiffness, the or each less stiff portion (19;35;46) being arcuate and centred
on the bearing axis, such that the reaction (R₁,R₂) to a load (P) acting along a radius
of the bearing includes substantial components (C₁₂,C₂₂) to each side of that radius
which are opposed to each other.
2. An assembly as claimed in Claim 1, characterised in that the housing (30) includes
the portion (35) which is less stiff than adjacent portions and is in line with that
radius.
3. An assembly as claimed in Claim 2, characterised in that the housing includes a
sleeve (17;44), the less stiff portion (19;46) being an integral part of the sleeve.
4. An assembly as claimed in any preceding claim, characterised in that the less stiff
portion is provided by a recess (18;34;45) which is radially spaced from the bearing
(11;31;41).
5. An assembly as claimed in Claim 4, characterised in that the recess (18;34) is
positioned radially outside of the bearing (11;31).
6. An assembly as claimed in any preceding Claim, characterised in that the less stiff
portion (19;35;46) extends longitudinally of the bearing (11;31;41) and is unsupported
at its ends.
7. An assembly as claimed in any preceding claim, characterised in that the radial
thickness (20;36;47) of the less stiff portion (19;35;46) is 0.15 × the sectional
height (16;33;43) of the bearing (11;31;41).
8. An assembly as claimed in any preceding claim, characterised in that the less stiff
portion (19;35;46) subtends laterally an angle (A) of 50° from the longitudinal axis
of the bearing (11;31;41).
9. An assembly as claimed in Claim 3, characterised in that means (21;48) fix the
position of the sleeve (17;44) in the housing (10;40).